A thermostatically controlled valve is described, for example, in German patent document No. 31 12 138 and comprises a valve body in which a thermostatically displaceable valve spindle is recited, this spindle carrying the valve member and having an extension passing through the valve seat and provided on the opposite side thereof from the main valve member with a limiting body which is greater in diameter than the neck connecting the body with the valve member and which, in the closed position of the valve, is spaced away from the valve seat and the passage therethrough.
In this system, the limiting body is so constructed that its cross section is smaller than that of the valve seat bore so that, when the body is shifted toward the bore, sufficient flow is provided.
This configuration is used so that with an increasing valve stroke, the throughput is not limited to a constant value, but rather is reduced from an upper limit. This serves, with large differences between the setpoint and actual values of the temperature of the valve, to ensure that the valve is only partly open and consequently, when the heating unit with which the valve is provided turns on initially or after a reduction in output for night-time use, all heating units can be supplied with the heating medium from the pump.
In other words, this prevents a sudden wide opening of one or more of the thermostatically controlled valves under these circumstances so that associated heating units receive all of the circulating heating medium to the exclusion of other heating units.
Another way of solving the problem has been proposed in the German patent document DE-OS No. 29 26 599 in which two heat sensors are provided, one of which operates with cold contact to ensure that the valve will completely or substantially completely close.
Another thermostatic control valve is described in German patent document DE-OS No. 25 14 040 in the form of a safety valve in which for cold contact and failure of the thermostat the valve passage is closed by the valve member but a limiting body of the type described can pass through the valve seat bore.
The publication Maintenance and Modernization Supervisor of September 1984 (vol. 4, No. 9) describes a thermostatically actuated valve in which the limiting body has a cross section greater than that of the valve seat bore so that in the maximum-opening position of the valve with respect to the main valve body, the limiting body can come to lie against the auxiliary seat formed at the opposite end of the valve seat bore or passage. With such a valve, upon removal of the thermostat head or a failure thereof, the valve spindle is removed into a position in which the limiting body blocks the body passage to prevent overheating of the room and serious energy losses.
In other words, even with failure of the thermostat head or its removal, throughtput through the valve is severely restricted or blocked.
In the German patent document No. 31 12 138, deposits can form in the valve-seat bores so that the limiting body cannot fully block the passage or insufficiently blocks the latter. This can prevent full closure of the valve.
A disadvantage of the latter system, however, is that a very precise adjustment and positioning of the limiting body relative to the valve seat body is required for effective operation and this precise adjustment is expensive to achieve because the limiting body is received with play in the passage so that exact orientation cannot be ensured by an arrangement on the housing.
In the system of German patent document DE-OS No. 29 26 599 another disadvantage can be ascertained. Here at least two heat sensors must be provided which, of course, involves expensive elements.
The valve of the Maintenance and Modernization Supervisor article mentioned previously also is expensive to fabricate and maintain and is difficult to mount and assemble. The limiting body must be inserted through the pipe or tube fittings into the valve housing and there attached to the valve stem which has previously been provided in the valve body.